what is an APO reflector telescope?

Question

is it different than a newtonian?

Answer 1

Actually, an apo is a refractor, not a reflector. Apo is short for apochromat. It means a lens with a higher level of color correction that a normal refractor (an achromat), typically at several times the price. An apo telescope lens can be either a doublet (two elements) or triplet (three elements). The triplets can have a shorter focal ratio for a given level of color correction. Modern apochromats are made with either calcium fluorite or a special-dispersion glass such as FPL-53 as one of the elements.

Answer 2

Simple lenses suffer from chromatic aberration i.e. you get colored fringes on bright objects. Early lenses (with multiple elements) that reduced the amount of chromatic aberration were called achromatic, meaning "no colour". Later, better, designs were called apochromatic to distinguish them from the achromats. Presumeably, apochromatic means "no colour, and this time we mean it". Newtonians don't suffer from chromatic aberration.

Answer 3

Not related to Newtonian at all.

APO is a TRIPLET design of REFRACTOR

Most refractors are duplets (two lenses)

That's all.

It's a REFRACTOR with a TRIPLET design (three lenses)

It's an improved or advance or alternative designed ACROMATIC refractor.